Enclosed please find 2 sets of tickets (If I were you, I would use two tickets ie without the words sets of), please acknowledge receipt of the tickets by signing and returning the duplicate copy of this letter.
Thank you.
Yours faithfully
For and on behalf of
ABC Company
_________________
Authorised signature
(Note: add the following to the duplicate copy:
Acknowledgement of receipt of 2 tickets
_______________________________
Mr. Steven Chan
Date: